1. Field
The present disclosure relates to light emitting devices, and more particularly, to semiconductor light emitting devices having stacked multiple light emitting diodes (LEDs).
2. Background
A light emitting diode (LED) is a forward-biased p-n junction generating photons by spontaneous electron-hole pair recombination. After decades of development, LED technology has been greatly advanced by improved materials, new manufacturing systems, and novel structures.
Due to the success and the great potential of the LED technology, LEDs have become one of the most important light sources for next generation illumination. Nevertheless, for illuminating applications, it is necessary to enhance the luminance (brightness) of LEDs.
Luminance is generally defined by the equation L=Φ/(AΩ). Where L is the luminance, Φ is the luminous flux (luminous power), A is the area of the light emitting surface, and Ω is the solid angle. To increase LED luminance, many contemporary devices have implemented higher operating current densities to increase the luminous flux Φ.
Unfortunately, increasing the operating current density may result in various undesired effects. One of the constraints of increasing the current density is the inability to effectively spread the electric current uniformly over the entire area. Consequently, the majority of current may only flow through a few isolated regions of the area. The isolated regions may exhibit current crowding and overheating. The heat, if not sufficiently dissipated, may cause premature degradation of the LED, decreasing its performance and life-span.
In addition to causing premature degradation of the LED due to overheating, a large current density may actually cause the luminous flux Φ to “roll over” and decrease the brightness of an LED, thus, decreasing the efficiency of the LED.
Accordingly, although contemporary LEDs have proven generally suitable for their intended purposes, they possess inherent deficiencies which detract from their overall effectiveness and desirability. As such, there exists a need for LEDs that occupy a small semiconductor footprint and provide a high luminance without the aforementioned deficiencies of contemporary devices.